This application claims the benefit of Korean Patent Application No. 2000-58114 filed on Oct. 4, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vertical cavity surface emitting laser (VCSEL), and more particularly, to a micro-lens built-in VCSEL in which a micro-lens is formed at a light emitting surface of the VCSEL.
2. Description of the Related Art
In general, VCSELs emit a light beam in a direction of a semiconductor material stack, and thus it is easy to be optically combined with another optical element and to be assembled into an apparatus. In addition, the VCSELs can also be manufactured to have a two-dimensional array structure and can be widely applied as a light source in optical transmission systems for applications such as optical communications or interfacing using optical signals, and in optical recording/reproducing optical heads.
Referring to FIG. 1, a conventional VCSEL includes a substrate 10, a lower reflector 11, an active layer 12, a high-resistance region 13 and an upper reflector 14 which are sequentially stacked on the substrate 10, an upper electrode 16 formed on a portion of the upper reflector 14 excluding a window 18 through which a laser beam is emitted, and a lower electrode 17 formed underneath the substrate 10.
Each of the lower reflector 11 and the upper reflector 14 is a distributed Bragg reflector (DBR) which is formed by alternately stacking semiconductor material layers having different refractive indices, and having an opposite doping type. That is, the substrate 10 and the lower reflector 11 are doped with the same n-type impurities and the upper reflector 14 is doped with p-type impurities.
The high-resistance region 13 guides the flow of current applied through the upper and lower electrodes 16 and 17 into the center of the active layer 12. The active layer 12 is a region where light is generated by a combination of holes and electrons from the upper and lower reflectors 14 and 11, which is induced by current applied across the upper and lower electrodes 16 and 17.
Light generated in the active layer 12 is reflected repeatedly between the upper and lower reflectors 14 and 11 and only a light beam having a wavelength in accordance with the resonance condition remains, and is emitted through the window 18.
In the conventional VCSEL having the aforementioned structure, the laser beam emitted through the window 18 has a predetermined radiation angle. Thus, when such a conventional VCSEL is adopted as a light source to be used as, for example, an optical transmission system using an optical cable, a condensing lens condensing a diverging beam emitted from the VCSEL is required between the VCSEL and the input terminal of the optical cable, so as to efficiently couple the light beam emitted from the VCSEL to the optical cable.
In addition, for a maximal optical efficiency of coupling the light beam emitted from the VCSEL to the optical cable, an additional device adjusting the position of the focus of the light beam emitted from the VCSEL and condensed by the condensing lens in an alignment processor and/or an actual operating process is needed.
When an optical system is constructed with the conventional VCSEL, many components are required, and there is a need to align the lens with the central optical axis of the laser beam emitted from the VCSEL, making an optical alignment structure complicated.
Accordingly, it is an object of the present invention to provide a micro-lens built-in vertical cavity surface emitting laser (VCSEL) in which the position of a micro-lens formed at a light emitting surface of the VCSEL can be varied, so that there is no need for a separate condensing lens and a separate device to adjust the focusing position of the laser beam in constructing an optical system with the VCSEL.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and other objects and advantages of the present invention are achieved by providing a micro-lens built-in vertical cavity surface emitting laser (VCSEL) comprising: a VCSEL portion emitting a laser beam in a direction in which semiconductor material layers are stacked; a micro-lens formed of a material capable of transmitting the laser beam emitted from the VCSEL portion; and an adjusting portion located between the VCSEL portion and the micro-lens adjusting a distance between the micro-lens and the VCSEL portion.
The above and other objects of the present invention are also achieved by providing that the adjusting portion comprises a piezoelectric material layer formed of piezoelectric polymer.
The above and other objects of the present invention are also achieved by providing that the VCSEL portion, the adjusting portion, and the micro-lens are each formed through separate processes and are then combined as a single unit by bonding.
The above and other objects of the present invention are also achieved by providing that the adjusting portion comprises a piezoelectric material layer formed of piezoelectric ceramic and the piezoelectric material layer has an aperture at its center through which a laser beam emitted from the VCSEL portion passes.
The above and other objects of the present invention are also achieved by providing that the VCSEL portion and the adjusting portion are formed as a single unit through continuous processes.
The above and other objects of the present invention are also achieved by providing that the piezoelectric material layer of the adjusting portion is formed as at least one layer.
The above and other objects of the present invention are also achieved by providing that the micro-lens built-in VCSEL further comprises an insulating layer between the VCSEL portion and the adjusting portion to electrically isolate the VCSEL portion and the adjusting portion.